**4.1.4 Analytical methods**

212 Biogas

before used. The average composition of the feedstock was shown in Table 2. Prior to being fed into the reactor, the substrate was diluted with tap water to a COD concentration of 10,000 mg L-1 in accordance with the required OLR (10 or 20 g COD L-1 d-1) in the hydrogenogenic reactor. Diluting UF whey permeate was maintained at a temperature 4°C

A 5 L UASB reactor with 4.5 L working volume (R1) was made of stainless steel and cylindrical in shape (Fig. 12). The reactor was constantly stirred at 50 rpm. The pH of mixed liquid in R1 was controlled automatically with 6 M NaOH. The temperature in R1 was maintained at 37°C by inserting the reactor in the thermostatic chamber. For start-up, the reactor was filled with undiluted UF whey permeate and was operated anaerobically at a batch mode. When hydrogen production reached its peak value, the bioreactor feeding mode was turned to a continuous one at a HRT of 24 h (OLR of 10 g COD L-1 d-1) or at a HRT of 12 h (OLR of 20 g COD L-1 d-1). The R1 performance (biogas production and composition in H2 and CH4, COD, Total Volatile Fatty Acids – TVFA concentration, pH) was monitored

**4.1.2 Hydrogen production process setup and operation** 

twice a week throughout the experimental period (84 days).

Fig. 12. Schematic of the two-stage fermentation system

**4.1.3 Methane production process setup and operation** 

A 5 L UASB reactor with 4.5 L working volume (R2) was made of stainless steel and cylindrical in shape (Fig. 12). The reactor was constantly stirred at 50 rpm. The pH of mixed liquid in R2 was controlled automatically at pH 7.2 (±0.05) with 6 M NaOH. The temperature in R2 was maintained at 37°C by inserting the reactor in the thermostatic chamber. The R2 was fed with the effluent from R1, which was collected in a 3 L container used as a storage tank which was constantly stirred at 50 rpm (Fig. 12). The temperature in

until used.

Determinations of COD, TSS, lactose, TVFA concentrations were carried out according to the Standard Methods for the Examination of Water and Wastewater (PN-74/C-04578.03; PN-78/C-04541; PN-67/A-86430; PN-75/C-04616.04). The measurement of the pH was continuously measured by the membrane electrodes, model ESAgP-301W, Eurosensor, placed in the liquid phase of reactor. Biogas composition (CH4, H2 and CO2) was analyzed by using an electronic analyzer (Gas Data GFM 430, Gas Data Ltd.). Biogas production was measured with a water displacement meter.
